Stealing Tuesday night’s show at the Democratic National Convention along with First Lady Michelle Obama was Julián Castro – the first Latino ever to deliver a convention keynote address. Yet while the 37-year-old mayor of San Antonio represents perhaps the most coveted bloc of swing voters in this presidential election, there’s one thing about the Stanford- and Harvard-educated Castro that might seem counterintuitive to non-Latinos: He doesn’t speak Spanish. He knows enough of it to recall his Mexican-born grandmother, as he did in his speech, telling him, “Que Dios los bendiga.” (May God bless you.) But he admits that your average white kid studying Spanish in high school probably speaks the language as well as he does.

That’s not exactly a plus for the Democrats, especially when the Republicans’ Latino standard bearer, Senator Marco Rubio, speaks fluent Spanish. Still, Castro is hardly an anomaly. A recent Pew Hispanic Center study found almost two-thirds of Latinos (or Hispanics) living in the U.S. are either bilingual or English-dominant. A majority (51%) of Latinos born in the U.S. are now English-dominant. That doesn’t mean all those Spanish-language ads Craig Romney is narrating for his dad’s presidential campaign are a waste of time. But it does suggest that the U.S.’s largest and fastest-growing minority group, despite its still strong connection to its Latin American roots, has become much more linguistically and culturally assimilated, a la Julián Castro, than mainstream America had anticipated. “For Hispanics,” notes Isaac Lee, president of news for Univision, the U.S.’s largest Spanish-language television network, “birth rates are now higher than immigration rates.”

That’s the kind of demographic shift that media executives as well as politicians ignore at their peril – which is why Lee and his boss, Univision President Cesar Conde, got together with ABC News President Ben Sherwood last year to brainstorm a new, English-language cable TV network targeted at Latinos. The still unnamed venture, announced in May, will debut online next month (Univision has already begun a social media outreach via English-language Tumblr and Twitter sites) and plans to hit the airwaves next summer with both news and lifestyle programming. It could mark one of the biggest developments in Latino-oriented media since networks like Telemundo, CNN en Español and the Miami-based Univision (now the U.S.’s fourth largest network overall) began broadcasting in the late 1900s. That’s especially true given the distribution muscle of the Disney corporation, which owns ABC.

The U.S.’s more than 50 million Latinos have long considered language a linchpin of their identity, whether they’re Mexican-Americans in Los Angeles or Cuban-Americans in New Jersey. That’s a big reason white politicos like Al Gore and George W. Bush have felt compelled to butcher Cervantes’ tongue on the stump. But the new linguistic trend is evidenced by the fact that English-language networks are partnering with Spanish-language counterparts, as NBC and Telemundo are doing with convention coverage, hoping to make English-speaking Latinos feel more included. “Even though more and more Hispanics live and work in English,” says Lee, himself a Colombian-American, “they still take pride in their culture and care about what’s going on with immigration and the places their parents and grandparents came from.”

The Black Entertainment Television (BET) network has thrived on much the same premise vis-à-vis African-Americans. It’s more than welcome, if not overdue, that major media like ABC and Univision have seen the light regarding Latinos, says Colombian-American journalist Viviana Hurtado, who authors the popular Wise Latina Club blog and is a regular columnist for Fox News Latino, an online version of what Univision and ABC are bringing to cable. “There is still this assumption that all Latinos are immigrants and Spanish-dominant,” says Hurtado, who argues that many younger, more English-proficient U.S. Latinos find it a condescending gimmick when English-language media and political campaigns address them in Spanish. “It’s a retro demographic model that’s more 2000 than 2012.”

Still, the new Univision/ABC network could be unsettling for some in the Latino community – not least the U.S. Spanish-language broadcasters who fret that their linguistic market could someday be as small as a starlet’s skirt on a telenovela (soap opera). But the bigger debate the venture reflects is whether bilingual education, upbringing and interaction still matter to Latinos, or whether Spanish should be de-emphasized in the home and classroom in favor of English (which Castro says was his experience growing up in San Antonio). In Miami, for example, where 60% of the population is Latino, there is a growing fear that neither Spanish nor English is the dominant Latino tongue – that a hybrid Spanglish has taken over, meaning less a bilingual generation than a sort of “alingual” cohort that doesn’t speak either language all that fluently.

Hurtado, who has a PhD in Latin American literature – “I do want to hold on to my parents’ culture and speak their language well,” she says – is certainly no foe of Spanish. She insists nonetheless that “for Latinos in this country, where English is the language of power, English proficiency is an imperative.” And yet, even so, they “want their news to be relevant to them,” says Lee. Univision/ABC research, he notes, shows that even for English-dominant Latinos, one of the most important stories from the shooting of Arizona Congresswoman Gabrielle Giffords last year was the young Mexican-American intern, Daniel Hernandez, who helped save her life and became a son-of-immigrants hero at a time when Arizona was enacting draconian anti-immigration laws.

That suggests that the Republican Party, which thanks to issues like immigration could lose the Latino vote as badly as it did in 2008, probably can’t count on Latinos becoming more conservative as they speak more English. In the end, Latinos seem to be saying, legislation trumps language.